A typically ambitious television series might see fit to introduce a significant new character every few episodes. By contrast, Game of Thrones, HBO's magisterial adaptation of George R. R. Martin's fantasy novel series A Song of Ice and Fire, periodically introduces entire cities. The show's first season featured, by my count, 21 principal characters along with dozens of subsidiary ones. And while a few were subtracted by the end of Season Two (stabbed, gored, beheaded, drenched in molten gold, etc.), many more were added.

Season Three, which premieres Sunday at 9 p.m. ET/PT, continues this relentless expansion. In the first four episodes (which are all I've seen), the mesmerizing mechanisms of the show's title sequence will wheel out the slave city of Astapor and the castle of Riverrun, and nearly a dozen new cast members will be introduced. (According to HBO, the season will feature a total of 257 named characters.) Indeed, Game of Thrones is approaching a laboratory-pure experiment in the amount of televisual information the human brain can process without sustaining permanent damage.

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(This is probably the place to note that if you have not watched the first two seasons of the show, it would be unwise to leap directly into the third—akin, perhaps, to showing up for a graduate seminar in quantum physics on one's first day of college. Be sensible: Start with Season One and take pleasure in watching the epic unfold.)

When we left Westeros at the end of Season Two, the land was in upheaval. Winterfell had been burned and the Stark children (Robb, Arya, Bran, Sansa, Rickon, Jon Snow) were scattered across the Seven Kingdoms and beyond. Their enemies, the Lannisters (Tyrion, Cersei, Tywin, the murderous boy-king Joffrey) retained an uneasy hold on King's Landing after rebuffing an attack by Stannis Baratheon, but the Northern rebellion led by Robb remained a looming threat. Farther north still, the White Walkers and their wights were shambling ominously en masse. To the East, Daenerys and her dragons had escaped Qarth intact. And who knows what became of Theon Greyjoy, the Stark betrayer torn between nature and nurture?

That last question will be answered, if somewhat elliptically, early in Season Three, with the belated appearance of a dastardly bastard (bastardly dastard?) who will be all too familiar to readers of the books. Also introduced will be king of the wildlings Mance Rayder (played by the great Ciaran Hinds) and his right hand, Tormund; Catelyn Stark's ineffectual brother and commanding uncle; a pair of new travelling companions for Bran; a handful of noble brigands; and the elder lady of the House Tyrell, played by Dame Diana Rigg, who proves she hasn't lost a step since The Avengers (not that one, this one) and her turn as Greatest Bond Girl of All Time. Did I leave anyone out? Doubtless so, but they'll arrive nonetheless.

Thus far, I would say that the third season appears to be better than the second, though it falls short of the near-perfection of the first (which had the not-to-be-repeated advantages of a principal protagonist and relatively linear plot). That this season looks to be an improvement on the last should come as no surprise, given that the third book of Martin's series is considerably better than its predecessor—indeed, the best of the five written thus far. (In recognition of its quality, Game of Thrones showrunners David Benioff and D. B. Weiss will be divvying its contents across two seasons.)

Season Two also made its share of unforced errors, both in terms of plot (the Qarth storyline, for instance, which was dull in the book, would have been better shrunk than padded) and in terms of casting (Stephen Dillane's Stannis seemed less a warrior than an angry clerk; Carice van Houten's Melisandre lacked mystery and charisma; and, compounding the mediocre subplot, pretty much every character in Qarth was badly off-key). That the season overcame such missteps is a testament to Benioff and Weiss—and, of course, to Martin.

Thus far, the third season appears to be better than the second, though it falls short of the near-perfection of the first. That this season looks to be an improvement on the last should come as no surprise, given that the third book is considerably better than its predecessor.

In addition to having richer material to work from, Season Three has thus far nailed its casting choices (Thomas Brodie-Sangster is particularly apt as Bran's elfin new friend Jojen Reed), even when it diverges somewhat from the novels' characterizations. Fans of the books will—of course—find our disappointments here and there. In the very first episode a major development takes place off-screen (almost certainly due to budgetary constraints) and a moderately important reveal is mishandled. There are, inevitably, plot contractions and omitted characters (which will prove a great kindness once the show tackles the exponential sprawl of books four and five). And on a few occasions, scenes are added with no evident purpose other than to demonstrate that Benioff and Weiss are themselves talented writers and not merely Martin's stenographers.

But judging from its first four episodes, Season Three of Game of Thrones will be a triumph—and one that, with luck, will continue to improve as it progresses. Benioff and Weiss have cited one scene in the third novel as a principal reason they wanted to tackle the show in the first place, and in a recent interview they allowed, "We think we pulled it off." Those familiar with the book should have no trouble guessing what scene they had in mind, nor that it appears to be coming (in keeping with the precedent of the last two seasons) in the penultimate episode. Its title? "The Rains of Castamere"—which was also the song that accompanied an early HBO teaser for the season. "In a coat of gold or a coat of red, a lion still has claws," goes the refrain. "And mine are long and sharp, my lord, as long and sharp as yours." Long and sharp indeed.